Date Calculator

Understanding the Gregorian Calendar

The Gregorian calendar is the most widely accepted and used calendar system around the world today. A typical year in this system has 365 days, with an extra day added to February during a leap year, making it 29 days instead of the usual 28. April, June, September, and November each have 30 days, while the remaining months have 31, except for February.

This calendar is an improved version of the Julian calendar, which itself was a refinement of the ancient Roman calendar. Initially, the Roman calendar was lunar-based and likely used moon phases to track time. The early version consisted of just 10 months totaling about 304 days, leaving winter months unaccounted for. This caused seasonal drift, prompting the need for more structured systems.

Later, the Romans introduced the Republican calendar, which aligned more closely with the solar year. It followed Greek methods, using 29.5-day lunar cycles and included leap months—January and February—to stay in sync with the seasons. Despite adjustments, the calendar still fell short of solar accuracy.

In 46 BC, Julius Caesar introduced the Julian calendar. He reformed the calendar year to 365 days and included a leap year every four years. This change eliminated reliance on moon sightings and aimed to align the calendar with the solar cycle. However, it wasn’t perfect—the calendar still drifted about 11 minutes per year, which added up over centuries.

By 1582, the Julian calendar was 10 days off track. To correct this, Pope Gregory XIII skipped 10 days—making October 4, 1582, followed immediately by October 15, 1582. He also revised leap year rules: only century years divisible by 400 would be leap years. This new system, known as the Gregorian calendar, significantly improved long-term accuracy, reducing calendar drift to about 1 day every 3,030 years.

Although adoption was gradual, the Gregorian calendar eventually became the global standard and remains the most commonly used date system today.

What Are Holidays?

Holidays are specific days when normal daily routines like work or school are paused, either fully or partially. These days may be recognized officially by law or celebrated traditionally based on cultural, national, or religious customs.

The meaning of “holiday” can vary by region. In the United States, “vacation” typically refers to paid time off, while “holiday” refers to nationally or culturally significant days. In other countries, such as the United Kingdom, “holiday” may refer to both vacation and observed public holidays.

Holidays usually mark important historical events, religious observances, or cultural celebrations. While some holidays—like Christmas and New Year’s Day—are recognized internationally, most countries have their own unique holidays. Even within a country, the way holidays are celebrated or observed can vary: some places shut down entirely, while others may only operate on a limited schedule.

For example, during Carnaval in Brazil, many businesses close for nearly a full week, except for those directly involved in the festivities or essential services.

Holiday Support in This Date Calculator

This Date Calculator primarily supports U.S. federal holidays, but it also allows you to manually add holidays specific to your country or personal calendar. You can even exclude certain holidays from calculations based on your preferences.

In the U.S., federal holidays are recognized nationwide, with non-essential federal offices closing and federal employees receiving paid leave. However, private companies are not legally required to observe these holidays—whether an employee gets the day off (or extra pay for working) depends on company policy.

Fixed vs. Floating Holidays

• Fixed holidays occur on the same date each year (e.g., New Year’s Day on January 1).

• Floating holidays are based on a specific weekday and month, meaning their actual date changes yearly.

For example:

• Martin Luther King Jr. Day is observed on the third Monday of January.

• Thanksgiving is celebrated on the fourth Thursday of November.

List of U.S. Federal Holidays

2025 U.S. Federal Holidays

2026 U.S. Federal Holidays